This is where your User eXperience (UX) developers are active within a dev-team, pushing the experience, behaviors and interactions. Pushing in this context means rapid evolution of a working UI. Imagine the UX saying “like this?” to a product owner, perhaps quickly followed by a reactive “no?, OK then, hang on …” clickety click “… how about this?”. To me at least, those clicks are on source code in some form, and when the product owner (or client) is happy and walks away, then the UX is able to commit to source control (providing they did not break any tests). Of course UX developers are not able to code all the way down the stack, so this ideal breaks for many technologies.